It is desirable to keep the size of film magazines used on cinema cameras as small as possible to facilitate easy handling. It is also desirable to maintain a constant center of gravity on cinema film cameras and magazines when these are used on remotely controlled pan/tilt heads so that the steering mechanisms associated with these installations will perform more effectively.
In the professional film industry, many new camera systems require critical balancing of the film camera and film magazine and the maintenance of this balanced state throughout the filming process as film is exposed. This is particularly true in gyroscopically stabilized camera systems. Additionally, magazine size is often a problem for operating the equipment in confined areas, since in many camera setups the film magazine is actually larger than the camera and lens being utilized. Lastly, it is often desired to load the camera with larger film loads (i.e. 1000 feet rather than 400 feet) so that longer uninterrupted sessions may take place without reloading of the camera.
In the past, conventional or "in-line" design film magazines were used having two separate film chambers. This meant that each chamber was of sufficient diameter to accommodate a full roll of film as the feed roll was transferred to the take-up roll. This resulted in a magazine having an overall length that was a little more than twice the diameter of the full film roll.
Subsequently, film magazines of the "displacement" type were developed. Magazines of this type have one chamber with the two spindles for the feed and take-up rolls being more closely spaced than in the "in-line" design. The spindle spacing is such that the volume initially occupied by the feed roll may later be occupied by the take-up roll as the camera is run. This approach results in a reduction in the length of the magazine of approximately 20%.
Neither of the foregoing designs, however, attempted to compensate in any way for the shift in the center of gravity of the loaded magazine during filming. In instances where maintaining a constant center of gravity is important, a separate assembly, either electrically driven or driven by a flexible cable from the camera, must be added. Typically a weight is driven by a feed screw in the opposite direction to the film travel in order to effect compensation. This extra assembly adds unwanted extra weight to the camera assembly and requires extra space for its installation.